1. Field of the Invention
This invention concerns a process for pretreating high temperature, petroleum containing formations so petroleum may be recovered therefrom by the use of temperature sensitive polymers.
2. Description of the Prior Art
Many subterranean, petroleum containing formations contain natural energy in the form of an active bottom water drive, solution gas drive, or a gas cap drive, in sufficient quantity to drive the petroleum through the formation to the production well from which it may be recovered to the surface of the earth. This phase of oil recovery, commonly known as primary recovery, recovers only a small portion of petroleum originally in place. When the natural energy source has been depleted, or in those formations where insufficient natural energy was originally present to permit primary recovery, some form of supplemental treatment is required to recover additional petroleum from the formation. Water flooding is by far the most economical and widely practiced supplemental recovery procedure and involves injecting water into the formation by one or more injection wells. The injection water displaces or moves the petroleum toward one or more production wells, where it is transported to the surface of the earth. Although considerable additional oil is usually recovered as a consequence of water flooding, as a general rule around 50% or more of the oil originally present in the formation remains in the formation after termination of water flooding.
It is well known in the field of oil recovery that the inclusion of even a small amount of a hydrophilic polymer in the flood water will increase the displacement efficiency by a substantial amount. Many materials have been proposed for use in polymer flooding oil recovery processes. Polyacrylamides and polysaccharides are very effective for use in oil recovery operations in dilute concentrations, i.e., from 200 to 1000 parts per million. Sulfated, ethoxylated alkyl or alkylaryl compounds are also effective in slightly higher concentrations.
Although it has been demonstrated in laboratory tests and published in the art, that the inclusion of a hydrophilic, viscosity increasing material in flood water will recover substantial amounts of additional petroleum from petroleum formations under ideal conditions, there are many conditions existing in subterranean petroleum containing formations which significantly degrades the performance of polymer solution injection. One of the most serious problems is the temperature limitation of most polymers. Most of the polymers proposed up to the present time for use in polymer flooding oil recovery processes will hydrolyze or otherwise deteriorate in aqueous solution when exposed to temperatures in excess of 150.degree. F-200.degree. F for long periods of time. Since a great many subterranean petroleum containing formations are hotter than 150.degree. F-200.degree. F, and since the polymer solution injected into a subterranean, petroleum-containing formation will ordinarily be in the formation for a period of many months or even years, the hydrolysis or other degradation of this polymer material reduces the polymer flooding recovery efficiency substantially.
In our U.S. Pat. No. 3,924,682 issued Dec. 9, 1975, there is disclosed a method for treating a subterranean oil formation to reduce it's temperature to permit use therein of a temperature sensitive surfactant.
In view of the foregoing discussion, it can be appreciated that there is a substantial, unfulfilled need for a method for conducting a polymer oil recovery process in subterranean, petroleum containing formations whose temperature is in excess of 150.degree. F-200.degree. F.